The present invention relates to a method and a control structure for torque feed-forward control of numerically controlled, elastic and thus oscillating multiple-mass systems such as machine tools, robots or the like.
Drive systems in which there is no rigid link between a motor and a load, for example the table of a machine tool, represent elastic and thus oscillating multiple-mass systems.
Conventionally, the methods for feed-forward control of the speed, acceleration and/or torque of such drive systems are based on the existence of a rigid link between the motor and the load. Such methods thus operate only subject to severe limitations in the case of elastic systems and have a high error component.
No suitable methods for feed-forward control of elastic systems have yet been described.
An object of the present invention is thus to provide a method as well as a control structure for torque feed-forward control of numerically controlled, elastic and thus oscillating multiple-mass systems, which take account of the elastic behavior between the motor and the load performed, e.g., using a processing device.
According to the present invention, this object is achieved by a method having the following method steps:
1.1 for reference-variable generation, parameters for impressing nominal motion states are estimated from an at least 4th-order reference model for motion control in that, derived from this in each axis control loop,
1.2 an axial nominal position angle is impressed via a nominal position value path in time with the interpolation,
1.3 an axial nominal rotation speed value is impressed via an advance rotation speed control path in time with the interpolation, and
1.4 an axial nominal drive torque value is impressed via an advance torque control path in time with the interpolation, in which case,
1.5 a spring toque which causes oscillations and is associated with the most pronounced natural frequency of the multiple-mass system is likewise derived from the reference model and compensated for by applying disturbance variables to the feed-forward torque control path.
A first advantageous embodiment of the method according to the present invention provides that the acceleration can be preset by additional degrees of freedom in time with the interpolation. This is made possible by the following further method step:
2.61 5th or higher order polynomials are used for fine interpolation in the reference model.
A further advantageous embodiment of the method according to the present invention provides that only the derivative of the jerk has discontinuities in the profile. This is made possible by the following further method step:
3.1 in the course of fine interpolation, the nominal values to be impressed are derived from profiles averaged over one interpolation interval.
A further advantageous embodiment of the method according to the present invention provides that averaging can be carried out with minimal computational complexity. This is achieved by the following further method steps:
4.1 the integrals required for averaging of the derivatives from the motion are transferred directly from the reference model,
4.2 the averaging of the motion is likewise carried out explicitly in that the individual contributions of all of the polynomials to the total integral of the motion are each added up and the difference between the sums is formed over one interpolation interval.
Furthermore, a control structure is proposed which is particularly suitable for achieving the object of the present invention since it allows effective implementation with little complexity. This control structure has the following elements:
5.1 an at least 4th-order reference model for motion control is provided for reference-variable generation of parameters for impressing nominal motion states, in which reference model, for each axis control loop,
5.2 a nominal position value path is provided for impressing axial nominal position angles in time with the interpolation,
5.3 an advance rotation speed control path is provided for impressing axial nominal rotation speed values in time with the interpolation, and
5.4 a feed-forward torque control path is provided for impressing axial nominal drive torque values in time with the interpolation, in which case
5.5 (e.g., an arrangement) is provided for applying disturbance variables to the feed-forward torque control path in order to compensate for a spring torque which causes oscillations and is associated with the most pronounced natural frequency of the multiple-mass system.
An advantageous embodiment of the control structure of the present invention provides that only the derivative of the jerk has discontinuities in the profile. The following further element is used for this purpose:
6.1 a fine interpolator is provided which interpolates the nominal values to be impressed from input variables averaged over one interpolation interval.